diff --git a/src/thermo.cpp b/src/thermo.cpp
index f32fd73ec5..9341c16e7a 100644
--- a/src/thermo.cpp
+++ b/src/thermo.cpp
@@ -688,7 +688,7 @@ void Thermo::modify_params(int narg, char **arg)
         for (int i = nlo - 1; i < nhi; i++) {
           if (i < 0) icol = nfield_initial + i + 1; // doesn't happen currently
           else icol = i;
-          if (icol < 0 || icol > nfield_initial - 1)
+          if (icol < 0 || icol >= nfield_initial)
             error->all(FLERR, "Invalid thermo_modify format argument: {}",
               arg[iarg + 1]);
           format_column_user[icol] = arg[iarg + 2];
@@ -706,7 +706,7 @@ void Thermo::modify_params(int narg, char **arg)
             icol = -1;
           }
         }
-        if (icol < 0 || icol > nfield_initial - 1)
+        if (icol < 0 || icol >= nfield_initial)
           error->all(FLERR, "Invalid thermo_modify format argument: {}", arg[iarg + 1]);
         format_column_user[icol] = arg[iarg + 2];
       }